1. Field of the Invention
The present invention relates to a method of growing a III-V group compound semiconductor on a substrate by an MOCVD method.
2. Description of the Related Art
In a conventional method of growing a compound semiconductor by a metal organic chemical vapor deposition method (MOCVD method) which is used for manufacturing a device such as a semiconductor laser and an LED, a V group hydride is used as a V group source, i.e., phosphine (PH.sub.3) is used as a phosphorus source, and arsine (AsH.sub.3) is used as an arsenic source. However, since these hydrides have very strong toxicity, high-cost peripheral equipment for such as an exhaust gas treatment is required for a safety operation. In addition, since these compounds are decomposed by only several percentages at a growth temperature of about 700.degree. C. in a normal MOCVD method, the utilization efficiency of the compounds is very low. For this reason, a high-quality thin film cannot be obtained unless the V group compounds are used several hundreds times more than III group compounds.
To solve problems in safety and utilization efficiency, various V group sources are examined.
Trialkyl V group compounds such as trimethylphosphine or trimethylarsine and monoalkyl V group compounds such as tert-butylphosphine or tert-butylarsine are examined (Appl. Phys. Lett., 48, 1531 (1986)). However, when these compounds are used, organic radicals are generated by thermal decomposition, and carbon atoms are undesirably mixed in a film to be grown. Especially, when trialkylphosphine is used, it is difficult to cause phosphorus deposition (G. B. Stringfellow "Organometallic Vapor-Phase Epitaxy" Academic Press, (1989) p. 35).
Phenyl V group compounds such as phenylphosphine and phenylarsine in which a phenyl group is bonded to a V group element are also examined. Since phenylphosphine and phenylarsine are resonantly stabilized, they are promising alternative sources that are expected that the carbon mixing to the film is substantially slight. As examples of MOCVD method using phenylarsine, growth of InAs is described in J. Cryst. Growth, 97, 489 (1989), and growth of GaAs is described in Chemtronics, 4, 78 (1989). In these examples, films can be obtained having excellent electrical characteristics that can cope with those of films obtained by using hydrides.
The above phenyl V group compounds, however, have a drawback that their thermal decomposition temperature is not largely different from that of hydrides, so that the utilization efficiency is disadvantageously low. Since the vapor pressures of the phenyl V group compounds are about 1 Torr at most at room temperature, bubblers in which these compounds are stored and supply tubes must be heated. In addition, these compounds cause side reactions in which they form adducts together with III group sources such as trimethylgallium to produce nonvolatile polymers having no contribution to the film growth (for example, Chemtronics, 4, 78 (1989)). Such side reactions are not only disadvantageous to the growth of compound semiconductors having an excellent surface, but they cause to degrade utilization efficiency of the V group compounds. To improve utilization efficiency of the V group source and to realize the growth of a high-quality compound semiconductor having an excellent surface morphology, the above drawbacks must be eliminated by chemically modifying the V group compounds.